The present invention relates to crosslinkable compositions formed from functionalized polyolefin powders which can be used in the slush molding process or in the thermoforming of sheets or in injection molding over an insert and more particularly to compositions based on functionalized polyethylene.
PVC or polyolefin powders are used to obtain skins by the process of molding by the free flow of powder onto a hot mold (hereinafter called the slush molding process). Slush molding is used for the manufacture of skins for dashboards, door panels and consoles in the automobile field. The powder is brought into contact with the hot mold, for example by the free flow techniquexe2x80x94the powder forms a skin by melting. These skins have a very soft feel and do not have residual stresses, which makes it possible, during the aging of the skin, to avoid the risk of the appearance of cracks caused by residual stresses relaxing.
Automobile dashboards are very often made of polyurethane and covered with a PVC skin obtained by the slush molding process. It is becoming less possible to use PVC because of the risk of pollution caused by its combustion. It is therefore necessary to develop polyolefin skins. Polypropylene skins have already been disclosed in the prior art but these skins are not sufficiently resistant to the high temperatures which can be found in automobiles out in the sun and with closed windowsxe2x80x94this resistance is measured by the hot creep.
Patent FR 2,721,319 discloses powder compositions for slush molding based on polypropylene and on ethylene-propylene rubber (EPR). The skins obtained do not have good creep resistance.
Polyolefin powder compositions have now been found which can be used in slush molding, in the thermoforming of sheets or in injection molding over an insert and which are crosslinkable thus, abrasion resistance and good creep resistance are obtained. The present invention is thus a crosslinkable composition formed from functionalized polyolefin powder comprising:
a functionalized polyolefin (A) having an MFI of at least 20 (190xc2x0 C./2.16 kg) containing an anhydride and/or epoxy functional group,
a product (B) having the role of crosslinking (A),
the composition having a particle size between 100 and 400 xcexcm.
According to a first embodiment of the invention, (A) is chosen from copolymers of ethylene and an unsaturated carboxylic acid anhydride and (B) is chosen from copolymers of ethylene and an unsaturated epoxide.
According to a second embodiment of the invention, (A) is chosen from copolymers of ethylene and an unsaturated carboxylic acid anhydride and (B) is chosen from polyamines adsorbed on a zeolite.
According to a third embodiment of the invention, (A) is chosen from copolymers of ethylene and an unsaturated epoxide and (B) is chosen from polyamines adsorbed on a zeolite.
In the slush molding process, the composition of the invention is converted into a skin on contact with the mold. The crosslinking takes place at a higher temperature than the melting point of (A) when it is carried out while the skin is in the mold, such as, for example, in the three embodiments mentioned above. The crosslinking takes place at a temperature between room temperature and the softening point of (A) when this crosslinking is initiated subsequently by a process of moisture diffusion through the skin, such as, for example, in the second and third embodiment, if it is chosen to allow the moisture to drive the amine from the zeolite after formation of the skin.